Here's a map showing the tiny portion of Queens in walking distance of subways. https://cwhong.carto.com/viz/6dfca01c-47e5-11e6-9fd3-0ee66e2.... And yes, it's almost all residential zoned, filled brick to brick with houses and apartments.
Based on this density map (https://www.google.com/search?q=pppulation+densoty+map+nyc&o...) I'd peg it at 35% of the city's pop.
